Cell therapy for male sexual dysfunctions: systematic review and position statements from the European Society for Sexual Medicine

Abstract Background Cell therapy (CT) is a form of regenerative medicine under investigation for the management of male sexual dysfunction (MSD). Aim We sought to perform a systematic review of published information on CT for MSD and provide an official position statements for the European Society for Sexual Medicine. Methods A comprehensive bibliographic search on the MEDLINE, Web of Science, Scopus, and Cochrane Library databases was conducted in February 2023. Articles were selected based on the Population, Intervention, Comparator, Outcome, Study design (PICOS) model if they included male patients (P) undergoing CT (I) with or without comparison with other treatments (C) and evaluated the impact of CT on sexual function (O). Quantitative data were reported as found in the original studies (S). Level of evidence and grade of recommendation according to the Oxford Centre for Evidence-Based Medicine were assigned to each statement. Outcomes Outcomes were determined based on assessment of erectile function, ejaculatory function, orgasmic function, sexual desire, and penile curvature. Results A total of 19 studies and 421 patients were included. Most articles (n = 12, 63%) were case series, whereas a minority of papers (n = 6, 32%) had a comparative group; only 2 articles reported randomized controlled trials (RCTs) and 1 article reported a post hoc analysis of RCTs. Most articles (16, 84%) investigated patients with erectile dysfunction (ED). Improvements in the International Index of Erectile Function–Erectile Function Domain (IIEF-EF) or the IIEF 5-item version (IIEF-5) were found in 11/15 (73%) studies, with mean increases in IIEF-EF, mean IIEF-5, and median IIEF-EF between 8 and 14 points, 2 and 9 points, and 4.5 and 6 points, respectively. Two papers (20%) evaluated men with Peyronie’s disease (PD). In both ot these articles penile curvature improvement and plaque volume reduction were described in all patients (n = 16, 100%). Objective measurements were performed in 1 study, which showed 10°-120° (15%-100%) curvature improvement and 90%-100% plaque reduction. Mild transient adverse events at the donor or administration sites were found in 7/16 (44%) papers on ED. Priapism was reported in one case (20%) and mild penile skin complications were reported in the majority of patients after CT for PD. No severe adverse events were described. Clinical Implications Although high-quality evidence is lacking, CT appears to have potential benefits from application in patients with ED or PD. Strengths and Limitations This report is to our knowledge the most comprehensive and up-to-date systematic review on the topic of CT for the management of MSD, including the position statements of the European Society for Sexual Medicine. Overall the assessment of available studies demonstrated low quality and significant heterogeneity. Conclusion Preliminary findings support potential efficacy and safety of CT in patients with ED or PD. Low-quality papers, high methodological heterogeneity, uncertainty about the magnitude of the beneficial effects, and lack of long-term data limit the available evidence.


Introduction
][3][4][5] However, in recent years we have been experiencing stagnation in the available therapeutic arsenal. 6Furthermore, the demand for "curative" and "definitive" treatments has always been a priority for patients suffering from MSD. 7 Regenerative medicine, which is based on treatments that promote the replacement or regeneration of damaged cells, tissues, or organs to restore normal function, has been emerging into this scientific and cultural context. 8This approach appears to be an interesting therapeutic option and a potential game changer in the management of patients with MSD. 6 Cell therapy (CT) refers to the transfer of cellular material into a patient for medical purposes.It includes stem cell-and non-stem cell-based therapies, covering multiple therapeutic areas, such as regenerative medicine, immunotherapy, and antineoplastic treatment. 9However, it is essential to underline that in the literature "stem cell therapy" often refers to therapies based on multicellular products containing multiple stem cells and non-stem cells obtained by extraction and processing of various tissues (eg, stromal vascular fraction, bone marrow aspirate). 9,10The key characteristics of stem cell are the ability to self-renew and the potential to differentiate into mature cell types.Based on the differentiation potential, these cells are classified as totipotent, pluripotent, multipotent, or unipotent, and, depending on the origin, they are distinguished in syngeneic, autologous, allogeneic, or xenogeneic cells. 11esenchymal stem cells (MSCs) are among the most frequently studied cell types for regenerative medicine.They are multipotent adult stem cells that can be isolated from different tissues, including bone marrow, adipose tissue, placenta, and umbilical cord. 12These MSCs exert their effect in therapeutic settings through several mechanisms of action.Differentiation and replacement of damaged cells is only one of many possible mechanisms and appears to be less relevant than the other possible roles of MSCs in the tissue repair process.Cell fusion, secretion of paracrine factors (eg, growth factors, cytokines, hormones), transfer of organelles (eg, mitochondria) or molecules through tunneling nanotubes, and transfer of signals via extracellular vesicles (eg, exosomes, microvesicles) are further demonstrated mechanisms of action of MSCs. 13n addition to the repairing effect, MSCs have shown antiinflammatory, immunomodulatory, angiogenic, antiapoptotic, mitotic, antifibrotic, and antioxidant properties. 14everal preclinical studies have explored the molecular and cellular mechanisms underlying MSC treatments and reported encouraging results on the possible use of stem cells in MSD. 10,15The first clinical trial on the topic, published in 2010 by Bahk et al, showed promising preliminary findings 16 ; however, few studies on humans have been conducted since then.Even today, this topic is the subject of great debate due to high costs, uncertainty about efficacy, and doubts regarding safety. 10Moreover, no specific recommendation on CT is available in the current European Association of Urology Guidelines on Sexual and Reproductive Health, 17 whereas according to the latest American Urological Association Guidelines, stem cells should be considered an investigational method in men with ED (conditional recommendation; evidence level: grade C). 18 The aim of the investigation reported here was to perform a systematic analysis of the current evidence regarding CT for MSD in humans and to provide position statements for their clinical use on behalf of the European Society for Sexual Medicine (ESSM).

General methodology
The protocol for this study was registered in the International PROSPERO (Prospective Register of Systematic Reviews) database.The data were reported according to the PRISMA (Preferred Reporting Items for Systematic Review and Metaanalysis) statement. 19

Search strategy
A comprehensive bibliographic search on the MEDLINE, Web of Science, Scopus, and Cochrane Library databases 20 was conducted in February 2023 to identify relevant studies.Different combinations of the following keywords were used to search for articles by title/abstract: "stem cell", "mesenchymal", "regenerative", "regeneration", "stromal vascular fraction", "bone marrow", "lipoaspirate", "sex", "sexual", "intercourse", "penis", "penile", "testicles", "testis", "testicular", "erectile", "erection", "impotence" "Peyronie", "curvature", "induratio", "recurvatum", "ejaculation", "ejaculatory", "orgasm", "desire", "libido".In addition, different associations of the following MeSH (Medical Subject Headings) terms were used to search for other relevant articles that may have escaped the previous search on the MEDLINE and Cochrane Library databases: "Stem Cells", "Coitus", "Erectile Dysfunction", "Penile Induration", "Premature Ejaculation", "Orgasm", "Libido", "Sexual Dysfunction, Physiological".The literature search was limited to English language publications and studies in humans.No restrictions for the date of publication were applied (Supplementary Data).References lists of the retrieved articles were used to identify additional significant studies.A further literature search based on the same parameters but restricted to the last 6 months before study completion was performed before submission to detect any new relevant papers published.

Study selection
The Population, Intervention, Comparator, Outcome, Study design (PICOS) model 21 was applied to define study eligibility.Articles were selected if they included male patients (P) undergoing CT (I) with or without comparison with other treatments (C), evaluating its impact on sexual function (O).Prospective and retrospective original studies were included (controlled and uncontrolled, randomized and nonrandomized).Given the presumed paucity of available papers, case reports, small case series (<10 cases), and post hoc analyses were also included.Conference abstracts, reviews, comments, letters to editors without original data, animal studies, and in vitro studies were excluded (S).
With the term "CT" we meant any treatment based on substances whose effects were presumed to derive mainly from the cells contained in them or their products.Plateletrich plasma treatment was excluded as it was considered an acellular therapy. 9Eligibility based on the assessment of the impact of CT on sexual function was defined as the description of erectile function, ejaculatory function, orgasmic function, sexual desire, or penile curvature using any type of validated or nonvalidated tool.Male fertility was excluded as an outcome because it falls within the reproductive rather than strictly sexual function.Articles evaluating the impact of stem cell transplantation for hematologic diseases on sexual function were excluded.Papers in which CT was part of combined treatment were included if a control arm allowed the effects of CT to be discerned.Studies with longer followup were chosen over articles with the same population and shorter follow-up; however, any missing data in the included articles were obtained from studies with shorter follow-up, if available.
The identification of relevant studies was conducted independently by 6 of the authors (I.S., N.P., E.F.-P., A.S., L.B., N.S.).An initial screening of titles and abstracts was performed.When it was not clear from the abstract whether the document might contain relevant data, the full article was evaluated.Thereafter, selected studies underwent a thorough full-text assessment to determine whether they were eligible for inclusion.Four senior authors (B.G.-G., J.R.-O., M.A., M.F.) supervised and resolved disagreements.No software or artificial intelligence was used in the search and selection of the articles.The bibliographies of the included studies were analyzed to find any additional relevant articles.

Data extraction and quality assessment
The following items were recorded: first author, publication year, country of origin, study period, study design, number of patients, age of patients, follow-up, clinical setting, type of CT, treatment protocol, efficacy outcomes, and safety outcomes.
The level of evidence (LoE) of all studies was evaluated according to the instructions provided by the Oxford Centre for Evidence-Based Medicine 2011, 22 ranging from 1 to 5 in decreasing order of evidence.The quality of the randomized RCTs, comparative nonrandomized studies, noncomparative studies, and case reports was determined with the Jadad scale, 23 Newcastle-Ottawa scale (NOS), 24 adapted NOS (without "selection of the nonexposed cohort" and "comparability of cohorts on the basis of the design or analysis" items), 25 and Murad scale, 26 respectively.Different cutoffs were arbitrarily chosen to classify the quality of the studies into low, intermediate, or high based on the scores obtained with these scales.A total score of 0-5 was considered low quality, 6 intermediate quality, and 7-9 high quality for the comparative nonrandomized studies.A total score of 0-2 was considered low quality, 3 intermediate quality, and 4-5 high quality for the RCTs.A total score of 0-4 was considered low quality, 5 intermediate quality, and 6-8 high quality for case reports.Finally, a total score of 0-3 was considered low quality, 4 intermediate quality, and 5-6 high quality for noncomparative studies.

Data synthesis and position statements
As a relatively low number of relevant papers with high heterogeneity in methodology and poor quality were expected, quantitative data were reported as found in the original studies.Sums, percentages, and means were used to summarize the quantitative data.The characteristics and main findings of all included articles were also reported narratively.
Position statements were formulated and approved by all authors following a discussion based on the available literature and the knowledge, and clinical experience of the authors.An LoE (range 1-5) and grade of recommendation (range A-D) according to the Oxford Centre for Evidence-Based Medicine were assigned to each position statement. 22,27hen the statement was derived from common sense rather than from study results, LoE and grade were replaced with a "Good Clinical Practice Statement."The terms "should" and "may" were used when the statement constituted a strong recommendation or suggestion, respectively.

ESSM position statements
1. Cell therapy for MSD should be considered a treatment under investigation and not offered outside of clinical trials approved by an Ethics Committee.(Good Clinical Practice Statement) 2. Patients should be informed regarding the limited evidence on the efficacy and safety of CT for MSD.Possible benefits, observed effects size, presumable timing and duration of effects, and potential adverse effects should be discussed in detail to set realistic expectations.(Level 3, Grade C) 3. Patients should be informed that CT for ED has been associated with improvements in erectile function and penile rigidity, but the clinical significance of the observed effects size is uncertain and the supporting evidence is limited.(Level 3, Grade C)

Reference
Study quality/risk of bias, total score a

CT in other MSD
A minority of studies (n = 3, 16%) evaluated the impact of CT on MSD effects other than ED. 30,32,41More specifically, 2 reported studies (11%) were focused on PD, 30,32 and 1 reported study (5%) investigated male patients with reduced sexual desire and testosterone levels. 41The main findings of the articles mentioned in this section are described in Table 3.

CT in PD
The 2 studies on PD included in this review investigated the effects of injection into the plaques of allogeneic placental matrix-derived mesenchymal stem cells 30 and autologous mesenchymal stem cells from the stromal vascular fraction. 32nrolled patients were in the chronic phase, with curvature between mild and 120 • .In both articles, penile curvature improvement and plaque volume reduction were described in all patients (100%). 30,32However, objective measurements were performed in only 1 study, which showed 10 • -120 • (15%-100%) curvature improvement at 6 weeks and 90%-100% plaque reduction. 30A reduction in the PD Questionnaire (PDQ) score was reported in the other study. 32No severe AEs were recorded.One case of priapism (1of 5 patients, 20%) 30 and mild penile skin complications in the majority of patients 32 were reported among the 2 studies.

CT in low sexual desire and testosterone levels
The articles on men with low sexual desire and testosterone levels described the effects of autologous adipose-derived mesenchymal stem cells infused through the intravenous route. 41At 12 months from baseline, statistically significant improvements in IIEF-EF and testosterone levels were reported; however, no increase was found scores for the IIEF-Sexual Desire questionairre.The authors recorded only nonserious AEs related to CT.In 3 articles on ED, testosterone levels were not reported to have changed significantly. 16,29,44exual desire was reported to have increased in some studies of ED patients 16,29,35 ; however, in other studies it did not change. 33,45

Discussion
This investigation is to our knowledge the most comprehensive and up-to-date systematic review thus far evaluating the use of CT in managing MSD.This study highlights the potential benefits and limitations of CT treatment in male sexual medicine and the characteristics of the literature available on the topic.Furthermore, the use of validated tools and a panel of experts has allowed the formulation of official ESSM position statements.Present data suggest a possible improvement of erectile function after CT; however, several considerations are necessary in this regard, and the available data should be interpreted with extreme caution.First, 2 of the 3 included RCTs did not find a statistically significant difference in IIEF scores between the examined groups. 16,37In addition, in a conference abstract, Hansen et al. 46 have recently presented the results of a randomized double-blind placebo-controlled phase 2 trial.Interestingly, this trial was an extension of the single-arm phase 1 study by Haahr et al. 34 This new RCT showed no statistical difference between groups in IIEF-5 and EHS at 1, 3, 6, and 12 months, contradicting the preliminary findings of the previous study.Hence, the vast majority of the available RCTs on the topic report discouraging results, highlighting the possibly that the positive findings in most other papers could simply be attributable to their low quality.
Moreover, the magnitude of the observed effects varied over a wide range and was almost never adequately investigated.Only 1 study reported MCID scores for the IIEF-EF (2, 5, and 7 for patients with mild, moderate, and severe baseline ED, respectively), 47 showing an improvement greater than or equal to othe MCID in only 33% of cases. 45imited evidence indicates that proper patient selection could be critical for the efficacy of CT in ED patients.Indeed, better outcomes were found in men with greater erectile function before cell administration, normal erectile function and urinary continence before radical prostatectomy, younger age, and lower prevalence of some comorbidities. 34,44The cell dose may also influence the efficacy of CT for ED; however, the included articles appear contradictory on this point. 37,399][40]42,43 This outcome is reasonable owing to the experimental nature of CT, due to which it was not proposed as a first line of treatment.On the other hand, this characteristic of the enrolled patients allows us to hypothesize that the selected patients were the most "difficult" to treat; consequently, the efficacy of CT may have been underestimated.In this context, it is important to underline that about half of the reported studies allowed or encouraged the concomitant use of ED medications with CT, 16,29,33,34,36,40,42 assuming a synergistic action between the treatments.According to reported details, several studies showed greater efficacy of CT when associated with pharmacotherapy, 16,29,33,34  In the 2 articles reporting studies in which CT alone was compared to the combination of CT with another regenerative therapy (ie, shockwaves or platelet lysate), a statistically significant improvement of IIEF-5 was found in both groups, with no significant difference between the groups. 36,38Therefore, the lack of a synergistic effect with other regenerative treatments can be speculated, but there are insufficient data to draw conclusions on the efficacy of CT compared to the other regenerative options.
Finally, some considerations should be addressed with regard to the timing of onset and the duration of effect after the administration of CT.Several studies reported improvement in IIEF starting 3-6 months after treatment [33][34][35][36][37][38][39][40][43][44][45] ; this latency period is reasonable given the regenerative nature of the therapy. Howeve, a not negligible number of reported studies showed improvement in erectile function within the first month, 16,28,29,35,36,[42][43][44][45] suggesting that more immediate mechanisms may exist and that some studies may have found effects at 3 months just because that was the first scheduled posttreatment evaluation.This hypothesis remains controversial since some articles reported significant improvement after 3-6 months but not at 1 month.33,34 On the other hand, some studies demonstrated a persistent beneficial effect on erectile function that lasted up to 12 months [33][34][35]37 ; conversely, a another reported study found worsening of erection between 6 and 12 months after the initial improvement.43 Such findings indicate that CT may be able to regenerate penile tissues but certainly cannot cure all causes of ED; these underlying causes can override the beneficial effect of the treatment over time as they continue to damage the tissues.Clear conclusions on the duration of the effect of CT cannot be drawn due to the lack of long-term studies; however, the probable temporary nature of benefits induced by CT is a fundamental point to take into account, as patients undergoing regenerative therapies are typically looking for a definitive solution.43 In ED patients, CT would seem safe; indeed, no severe AEs were recorded in the studies evaluated.Only mild local complications occurred at the donor and recipient sites.31,[34][35][36]39,43,45 However, it is essential to point out that small samples size of included articles and lack of long-term data prevent the drawing of conclusions on uncommon side effects and possible late complications (including cancer risk).
Surgery remains the therapy of choice in men with chronic PD who require active therapy for penile curvature.Nevertheless, if patients desire a noninvasive approach, intralesional treatment with collagenase Clostridium histolyticum or interferon-α2b may be an option. 17Since Clostridium histolyticum was withdrawn from the European market 48 and the use of interferon-α2b was associated with multiple AEs and high costs, 49 other substances are under investigation for intralesional therapy, including CT, plateletrich plasma, and hyaluronic acid. 50nteresting preliminary data were found regarding the application of CT in chronic PD.The mechanism of action of CT in this clinical setting remains unclear.Preclinical studies demonstrated the antifibrotic activity of stem cells.More specifically, they appear to be able to decrease collagen deposition, reduce the number of myofibroblasts, diminish the expression of tissue inhibitors of metalloproteinases, enhance the expression of matrix metalloproteinase, and inhibit several fibrosis-related cellular signaling pathways. 15,51oth clinical studies on PD that we investigated showed significant plaque size reduction and penile curvature improvement in all patients, in some cases with complete resolution. 30,32However, the data supporting such apparently promising results derive from single-arm studies characterized by low quality and high risk of bias, which need to be confirmed in robust RCTs.Only 1 case of a patient with priapism and mild local AEs was recorded after CT for PD, 30,32 but again, the reported safety data for this treatment are currently very limited and need to be confirmed with adequate RCTs.
Interestingly, 1 article on PD reported an enrolled apatient with penile pain without curvature. 30The outcomes of this patient were not described in the paper, but this case suggests a possible use even in the acute phase of the disease.Stem cells have an anti-inflammatory and antifibrotic effect 14 ; therefore, CT in acute PD could reduce pain and prevent/attenuate fibrosis.However, this conclusion remains a speculation that needs to be confirmed with appropriate clinical trials.
The impact of CT on sexual desire and testosterone levels was specifically investigated by only one study, 41 while other papers reported only scattered data in this regard. 16,29,33,35,44,45The results on the topic are contradictory and the evidence is too low to draw any kind of conclusions.
Despite the results obtained, the data reported here should be read and interpreted with the consideration of several limitations.First of all, the studies included are relatively few and overall have a small sample size, short follow-up, and uncontrolled design, showing a low quality.On the other hand, the heterogeneity of cells used; preparation methods, doses, administration protocols; and tools to evaluate the outcomes make it difficult to compare different studies and draw general conclusions.All of the above factors prevent the performance of a meta-analysis (excluded a priori) and affect the formulation of position statements.Furthermore, it should be considered that many of the available studies were designed to evaluate the feasibility or safety of CT as the primary outcome; this approach limits the reliability of the efficacy data.Finally, according to the details reported on ClinicalTria ls.gov, it is possible to hypothesize that the available evidence suffers from significant bias resulting from the suspension of several studies due to lack of funding, recruitment difficulties or poor efficacy, and consequent nonpublication of related data.
A particular effort should be made to develop well-designed RCTs on CT for MSD.Placebo-arm, blinding, large sample size, and extended follow-up are essential characteristics for future studies to offer an adequate LoE.Another fundamental point is to evaluate sexual outcomes only with validated and commonly used questionnaires to facilitate comparability of study results.The magnitude of the effects should be explored appropriately to understand if they are clinically significant.Preparation methods, doses, and administration protocols of CT should be standardized to make comparisons between different articles more reliable.Comparative studies between different types of cells should be developed.Longterm side effects (including the risk of cancer, especially in patients with a personal history of previous tumors), time required for the onset of the effect, and duration of any benefit obtained should be evaluated adequately in future papers.Research to determine the predictors of better outcomes after CT should be planned to facilitate the choice of the best candidates for this treatment.Finally, future studies on CT should also investigate other fields of male sexual health that are partially or totally unexplored, such as PD, premature ejaculation, orgasmic dysfunctions, and sexual desire disorders.
Unfortunately, the future of ongoing CT research currently does not look bright.High research costs, difficulty obtaining approval from local Ethics Committees, and legal issues to patent CT technology are significant obstacles.These factors may explain why research on the topic is progressing so slowly in the last decades and will likely prevent many high-quality studies from being conducted in the coming years.
In conclusion, preliminary findings are available in favor of efficacy and safety of CT in patients with ED or PD, suggesting a potential application of CT in these patients.However, the supporting evidence is very limited, due to low-quality papers, consistent methodological heterogeneity, uncertainty about the magnitude of the supposed beneficial effects, and lack of long-term data.Consequently, CT should be considered a treatment under investigation and offered only within clinical trials.Further research is needed to improve the knowledge, standardize the treatment, formulate strong recommendations based on high-quality evidence, and ultimately implement CT in regular clinical practice.

Figure 1 .
Figure 1.PRISMA flow diagram for study selection.
papers, respectively.Analysis of study quality revealed a median (range) NOS score of 5 (4-5) for the comparative nonrandomized studies (overall low quality), a median (range) Jadad scale score of 3 (2-4) for the RCTs (overall intermediate quality), a median (range) adapted NOS score of 4 (3-5) for the comparative nonrandomized studies (overall intermediate quality), and a Murad score of 3 for the only case report included (low quality).The study quality and LoE assessment was detailed in Table

Figure 2 .
Figure 2. Cell retrieval sites in studies on erectile dysfunction (ED).

Table 1 .
Main characteristics of studies.
Abbreviations: CT, cell therapy; ESWT, extracorporeal shock wave therapy; NA, not available; RCT, randomized controlled trial.a First author.b Last visit, unless otherwise stated.c Mean. d Range.e Median.

Table 2 .
Quality and level of evidence of studies.

Table 3 .
Clinical setting, administered CT, and main findings of studies.